Vacuum cleaners are designed to separate dirt and dust from an airflow. In a typical vacuum cleaner an airflow generator (for example, a motor and fan unit) generates an airflow which draws dirt- and dust-laden air into the vacuum cleaner through a dirty air inlet. The airflow then passes through a form of separating apparatus to remove dirt and dust from the airflow. Some vacuum cleaners make use of a porous bag through which the dirty air is sucked so that the dirt and dust is retained in the bag while cleaned air is exhausted to the atmosphere. In other vacuum cleaners, cyclonic separators are used to separate dirt and dust from the airflow.
Irrespective of the type of separating apparatus used, there is a risk of a small amount of dirt and dust passing through the separating apparatus and being carried to the airflow generator. It is undesirable for dirt and dust particles to pass through the fan of an airflow generator because the fan may become damaged or may operate less efficiently. In order to reduce this problem, some vacuum cleaners include a fine filter in an airflow path between the separating apparatus and the airflow generator. This filter is commonly known as a pre-motor filter and is used to extract fine dirt and dust particles remaining in the airflow after it has passed through the separating apparatus.
During normal operation of a vacuum cleaner, fine dirt and dust may be deposited on the pre-motor filter and, after a period of time, it could become blocked. Blockages reduce the efficiency at which a vacuum cleaner operates. Therefore, the pre-motor filter will occasionally need to be replaced or cleaned in order to maintain the performance of the vacuum cleaner. In order to allow cleaning or replacement of the pre-motor filter, it is common for such filters to be removable from a vacuum cleaner.
It is also known to provide a filter downstream of the airflow generator. This is known as a post-motor filter, and is typically employed to filter carbon dust which may be generated by brushes on the motor, as well as allergens and any microscopic particles of dirt and dust remaining in the airflow. After a period of use, the post-motor filter may need to be cleaned or replaced. Typically, the post-motor filter will need such attention much less frequently than does the pre-motor filter.
It is beneficial to permit the user to be able to monitor the condition of both the pre-motor filter and the post-motor filter, and to remove and replace them as required. To this end, access to both of the filters may be provided. However, it is more important that the user checks the pre-motor filter as it gets dirtier than the post-motor filter. By providing access to both filters, there is a risk that the user will check only the post-motor filter and neglect the pre-motor filter. This could lead to detrimental performance of the cleaner, and possibly even damage to the motor and fan.